This application is based on Application No. 2001-344878, filed in Japan on Nov. 9, 2001, the contents of which are hereby incorporated by reference.
This invention relates to a semiconductor device mounted on movable bodies such as vehicles.
FIG. 3 shows an example of a conventional semiconductor device mounted on moving bodies. In FIG. 3, 1 is a semiconductor device electrically connected via bonding wires 7 within a casing 5, and forms an electric circuit by being connected via the bonding wires 7 to electrodes 6 disposed in the lateral walls of the casing 5. The semiconductor device 1 is soldered by a solder 3a onto an insulation matrix being soldered by a solder 3b onto a bottom 4 of the casing 5. 8 is a gel resin or gelatious resin filled in the casing 5 and serves for insulation covering of the semiconductor device 1 and the bonding wires 7. 10 is a board-shaped vibration limiting member for limiting the vibrations of the gel resin 8 by being attached to the gel resin 8 and is connected to a lid 9 of the semiconductor device that is secured to both of the lateral walls of the casing 5 via rod-shaped supporting members 15. The vibration limiting member 10 is provided with a plurality of perforations 10a extending therethrough for draining the air mingled in the gel resin 8 during the filling of the gel resin 8 into the casing 5.
A semiconductor device thus composed is shaken by vibrations of a movable body onto which the semiconductor device is mounted because it is used by being mounted onto movable bodies. When the casing 5 of the semiconductor device is shaken, the gel resin 8 filled in the casing 5 is shaken as well. The amplitudes of the vibrations of the gel resin 8 are smaller in the portions of the resin positioned close to the walls of the casing 5 including the bottom and the lateral sides than those in the portion of the resin positioned in the central section of the casing 5 away from the walls, with those in the portion at the surface of the gel resin 8 at the top of the casing 5 being maximum. The problem of the break of the bent sections at both sides of the loops of the bonding wires 7 due to a repetitive stress under which the bent sections are put with the vibrations of the gel resin 8 is prevented by the limitation of the vibrations of the gel resin 8 through the vibration limiting member 10 that is connected to the lid 9 of the semiconductor device and is placed on the gel resin 8 to attach to the surface of the resin.
Yet, in semiconductor devices mounted onto moving bodies, such as vehicles, the gel resin 8 filled in the casing 5 tends to swell not only by the vibrations of the vehicle body but also by an effect of the heat generated at the engine room of the vehicle body and in the surrounding atmosphere, and in particular, by the heating of the semiconductor device. In such a situation, the swollen gel resin 8 overflows through a plurality of the perforations 10a formed in the vibration limiting member 10. The plurality of the perforations 10a therefore serve not only for the purging of the air mingled in the gel resin 8 when filling the gel resin 8 into the casing 5 but also for the release of the gel resin 8 that has swollen upon heating.
For the purpose of purging the air mingled in the gel resin 8 when filling the gel resin 8 into the casing 5, it is desirable that the exposed area of the gel resin 8 at its surface is extended by forming as many perforations 10a as possible. While, for the purpose of limiting the vibrations of the gel resin 8, the number and the size of the perforations 10a must be set at the levels that allow the vibration limiting member 10 to have a large area of contact with the gel resin 8. It is therefore difficult to attain an efficient or a perfect extraction of air from the gel resin 8 contained in the casing 5 by simply forming a plurality of perforations in the vibration limiting member 10 as done so far.
Further, in the system in which the vibration limiting member 10 is secured, such problems as the lodging of the bonding wires 7 and the cracking of the gel resin 8 could occur due to a flow of the gel resin 8 positioned close to the bonding wires 7 toward the perforations 10a, if the gel resin 8 in the casing 5 that has swollen due to the heating of the semiconductor device overflows through a plurality of the perforations 10a formed in the vibration limiting member 10.
The present invention therefore has as its object the provision of a semiconductor device, in which it is possible to drain the air mingled in a gel resin efficiently and perfectly.
With the above object in view, the semiconductor device comprises a casing, a semiconductor device electrically connected by bonding wires and a gel resin filled in the casing and serves for insulation covering of the semiconductor device and the bonding wire. The device further comprises a board-shaped vibration damper in contact with the gel resin and is provided with a plurality of perforations each having an air inlet and an air outlet for the purpose of air extraction during the filling of the gel resin. The sectional area of the perforations is tapered and larger at the inlet than at the outlet, thus causing the perforations to have the form of a substantially conical trapezoid as a whole.
Therefore, the air mingled within a gel resin of the semiconductor device can be efficiently and well purged.